Japanese patent laid-open No. 2003-167151 discloses a fusion splicer comprising: a main body; a pair of arc electrodes arranged on the main body; holders attached to stages provided on the main body and used for holding optical fibers; and a windbreak cover, which allows free movement of closing/opening, for covering the arc electrodes and the stages. A feed slot for introducing an optical fiber into a holder is formed at each side of the windbreak cover, and an elastic body is provided so as to close an upper part of the feed slot. On the other hand, an elastic body for closing a lower part of the feed slot is provided at each side of the main body at a part corresponding to the elastic body of the housing in the state where the windbreak cover is closed. And the fusion splicer is structured such that an optical fiber is inserted between the elastic body of the windbreak cover and the elastic body of the housing in the state where the windbreak cover is closed.